Base station device, terminal device and communication method

ABSTRACT

In a terminal, a control unit transmits a bundle response signal using a resource in a basic region of an uplink control channel in an uplink unit band of a unit band group when no error is detected in each of a plurality of pieces of downlink data of the unit band group, the uplink control channel in the uplink unit band being associated with a downlink control channel in a basic unit band that is a downlink unit band in which a broadcast channel signal including information relating to the uplink unit band is transmitted, and the control unit transmits the bundle response signal using a resource in an additional region of the uplink control channel when an error is detected in each of the plurality of pieces of downlink data.

TECHNICAL FIELD

The present invention relates to a terminal apparatus and retransmissioncontrol method.

BACKGROUND ART

3GPP LTE adopts OFDMA (Orthogonal Frequency Division Multiple Access) asa downlink communication scheme.

In a radio communication system to which 3GPP LTE is applied, a basestation transmits a synchronization signal (Synchronization Channel:SCH) and broadcast signal (Broadcast Channel: BCH) using predeterminedcommunication resources. A terminal secures synchronization with thebase station by catching an SCH first. After that, the terminal acquiresparameters specific to the base station (e.g., frequency bandwidth) byreading BCH information (see Non-Patent Literatures 1, 2 and 3).

Furthermore, after completing the acquisition of parameters specific tothe base station, the terminal makes a connection request to the basestation to thereby establish communication with the base station. Thebase station transmits control information to the terminal with whichcommunication is established via a PDCCH (Physical Downlink ControlCHannel) as required.

The terminal then makes a “blind decision” on each of a plurality ofpieces of control information included in the received PDCCH signal.That is, the control information includes a CRC (Cyclic RedundancyCheck) portion and this CRC portion is masked with a terminal ID of thetransmission target terminal in the base station. Therefore, theterminal cannot decide whether or not the control information isdirected to the terminal until the CRC portion of the received controlinformation is demasked with the terminal ID of the terminal. When thedemasking result shows that the CRC calculation is OK in the blinddecision, the control information is decided to be directed to theterminal.

Furthermore, in 3GPP LTE, ARQ (Automatic Repeat Request) is applied todownlink data from a base station to a terminal. That is, the terminalfeeds back a response signal indicating the error detection result ofthe downlink data to the base station. The terminal performs a CRC onthe downlink data and feeds back ACK (Acknowledgment) when CRC=OK (noerror) and NACK (Negative Acknowledgment) when CRC=NG (error present) asa response signal to the base station. An uplink control channel such asPUCCH (Physical Uplink Control Channel) is used for feedback of thisresponse signal (that is, ACK/NACK signal).

Here, the control information transmitted from the base station includesresource allocation information including resource information or thelike allocated by the base station to the terminal. The aforementionedPDCCH is used for transmission of this control information. This PDCCHis made up of one or a plurality of L1/L2 CCHs (L1/L2 Control Channels).Each L1/L2 CCH is made up of one or a plurality of CCEs (Control ChannelElements). That is, a CCE is a base unit when control information ismapped to a PDCCH. Furthermore, when one L1/L2 CCH is made up of aplurality of CCEs, a plurality of continuous CCEs are allocated to theL1/L2 CCH. The base station allocates an L1/L2 CCH to the resourceallocation target terminal according to the number of CCEs necessary toreport control information for the resource allocation target terminal.

The base station then transmits control information mapped to physicalresources corresponding to the CCEs of the L1/L2 CCH.

Here, each CCE has a one-to-one correspondence with a component resourceof the PUCCH. Therefore, the terminal that has received the L1/L2 CCHidentifies component resources of the PUCCH corresponding to CCEs makingup the L1/L2 CCH and transmits a response signal to the base stationusing the resources. However, when a plurality of CCEs where there arecontinuous L1/L2 CCHs are occupied, the terminal transmits a responsesignal to the base station using one of the plurality of PUCCH componentresources (e.g., PUCCH component resources corresponding to a CCE havingthe smallest index) corresponding to the plurality of respective CCEs.This allows downlink communication resources to be used efficiently.

As shown in FIG. 1, a plurality of response signals transmitted from aplurality of terminals are spread by a ZAC (Zero Auto-correlation)sequence having a Zero Auto-correlation characteristic, Walsh sequenceand DFT (Discrete Fourier Transform) sequence on the time axis andcode-multiplexed within the PUCCH. In FIG. 1, (W₀, W₁, W₂, W₃)represents a Walsh sequence having a sequence length of 4 and (F₀, F₁,F₂) represents a DFT sequence having a sequence length of 3. As shown inFIG. 1, in the terminal, a response signal such as ACK or NACK isprimary-spread by a ZAC sequence (sequence length 12) into a frequencycomponent corresponding to 1 SC-FDMA symbol on the frequency axis first.Next, the primary-spread response signal and the ZAC sequence as areference signal are secondary-spread in association with a Walshsequence (sequence length 4: W₀ to W₃) and DFT sequence (sequence length3: F₀ to F₃) respectively. Furthermore, the secondary-spread signal isfurther transformed into a signal having a sequence length of 12 on thetime axis through IFFT (Inverse Fast Fourier Transform).

A CP is added to each signal after the IFFT and a one-slot signal madeup of seven SC-FDMA symbols is thereby formed.

Response signals transmitted from different terminals are spread using aZAC sequence corresponding to different cyclic shift indices ororthogonal code sequences corresponding to different sequence numbers(Orthogonal cover Index: OC index). The orthogonal code sequence is acombination of a Walsh sequence and a DFT sequence. Furthermore, theorthogonal code sequence may be referred to as a “block-wise spreadingcode.” Therefore, the base station can demultiplex a plurality ofcode-multiplexed response signals using conventional despreading andcorrelation processing (see Non-Patent Literature 4).

However, since each terminal makes a blind decision on a downlinkallocation control signal directed to the terminal in each subframe, theterminal side does not necessarily succeed in receiving the downlinkallocation control signal. When the terminal fails to receive thedownlink allocation control signal directed to the terminal in a certaindownlink unit band, the terminal cannot even know whether or not thereis downlink data directed to the terminal in the downlink unit band.Therefore, when failing to receive the downlink allocation controlsignal in a certain downlink unit band, the terminal cannot evengenerate a response signal for the downlink data in the downlink unitband. This error case is defined as a DTX of response signal (DTX(Discontinuous transmission) of ACK/NACK signals) in the sense thattransmission of the response signal is not performed on the terminalside.

Furthermore, standardization of 3GPP LTE-advanced which realizes fastercommunication than 3GPP LTE has started. A 3GPP LTE-advanced system(hereinafter, may also be referred to as “LTE-A system”) follows the3GPP LTE system (hereinafter also referred to as “LTE system”). In orderto realize a downlink transmission rate of a maximum of 1 Gbps or above,3GPP LTE-advanced is expected to introduce base stations and terminalscapable of communicating at a wideband frequency of 40 MHz or above.

In an LTE-A system, to realize communication at an ultra-hightransmission rate several times as fast as the transmission rate in anLTE system and backward compatibility with the LTE systemsimultaneously, a band for the LTE-A system is divided into “unit bands”of 20 MHz or less, which is a support bandwidth for the LTE system. Thatis, the “unit band” is a band having a width of maximum 20 MHz anddefined as a base unit of a communication band. Furthermore, a “unitband” in a downlink (hereinafter referred to as “downlink unit band”)may be defined as a band divided by downlink frequency band informationin a BCH broadcast from the base station or by a spreading width whenthe downlink control channel (PDCCH) is spread and arranged in thefrequency domain. On the other hand, a “unit band” in an uplink(hereinafter referred to as “uplink unit band”) may be defined as a banddivided by uplink frequency band information in a BCH broadcast from thebase station or as a base unit of a communication band of 20 MHz or lessincluding a PUSCH (Physical Uplink Shared CHannel) region near thecenter and PUCCHs for LTE at both ends. Furthermore, in 3GPPLTE-Advanced, the “unit band” may also be expressed as “componentcarrier(s)” in English.

The LTE-A system supports communication using a band that bundlesseveral unit bands, so-called “carrier aggregation.” Since throughputrequirements for an uplink are generally different from throughputrequirements for a downlink, in the LTE-A system, studies are beingcarried out on carrier aggregation using different numbers of unit bandsset for an arbitrary LTE-A system compatible terminal (hereinafterreferred to as “LTE-A terminal”) between the uplink and downlink,so-called “asymmetric carrier aggregation.” Cases are also supportedwhere the number of unit bands is asymmetric between the uplink anddownlink and the frequency bandwidth differs from one unit band toanother.

FIG. 2A and FIG. 2B are diagrams illustrating asymmetric carrieraggregation and its control sequence applied to individual terminals.FIG. 2B shows an example where the bandwidth and the number of unitbands are symmetric between the uplink and downlink of a base station.

In FIG. 2B, a setting (configuration) is made for terminal 1 such thatcarrier aggregation is performed using two downlink unit bands and oneuplink unit band on the left side, whereas a setting is made forterminal 2 such that although the two same downlink unit bands as thosein terminal 1 are used, the uplink unit band on the right side is usedfor uplink communication.

Focusing attention on terminal 1, signals are transmitted/receivedbetween an LTE-A base station and LTE-A terminal making up an LTE-Asystem according to the sequence diagram shown in FIG. 2A. As shown inFIG. 2A, (1) terminal 1 establishes synchronization with the downlinkunit band on the left side at a start of communication with the basestation and reads information of the uplink unit band which forms a pairwith the downlink unit band on the left side from a broadcast signalcalled “SIB2 (System Information Block Type 2).” (2) Using this uplinkunit band, terminal 1 starts communication with the base station bytransmitting, for example, a connection request to the base station. (3)Upon deciding that a plurality of downlink unit bands need to beallocated to the terminal, the base station instructs the terminal toadd a downlink unit band. In this case, however, the number of uplinkunit bands does not increase and terminal 1 which is an individualterminal starts asymmetric carrier aggregation.

Furthermore, in LTE-A to which the aforementioned carrier aggregation isapplied, the terminal may receive a plurality of pieces of downlink datain a plurality of downlink unit bands at a time. In LTE-A, studies arebeing carried out on channel selection (also referred to as“multiplexing”) as one of transmission methods for a plurality ofresponse signals for the plurality of pieces of downlink data. Inchannel selection, not only symbols used for a response signal but alsoresources to which the response signal is mapped are changed accordingto a pattern of error detection results regarding the plurality ofpieces of downlink data. That is, channel selection is a technique thatchanges not only phase points (that is, constellation points) of aresponse signal but also resources used to transmit the response signalbased on whether each of response signals for a plurality of pieces ofdownlink data received in a plurality of downlink unit bands as shown inFIG. 3B is ACK or NACK (see Non-Patent Literatures 5 and 6).

Here, ARQ control by channel selection when the above-describedasymmetric carrier aggregation is applied to a terminal will bedescribed using FIG. 3B.

When, for example, a unit band group made up of downlink unit bands 1and 2, and uplink unit band 1 (which may be expressed as “componentcarrier set” in English) is set for terminal 1 as shown in FIG. 3B,downlink resource allocation information is transmitted from the basestation to terminal 1 via respective PDCCHs of downlink unit bands 1 and2 and then downlink data is transmitted using resources corresponding tothe downlink resource allocation information.

When the terminal succeeds in receiving downlink data in unit band 1 andfails to receive downlink data in unit band 2 (that is, when theresponse signal of unit band 1 is ACK and the response signal of unitband 2 is NACK), the response signal is mapped to PUCCH resourcesincluded in PUCCH region 1 and a first constellation point (e.g.,constellation point (1,0)) is used as a constellation point of theresponse signal. On the other hand, when the terminal succeeds inreceiving downlink data in unit band 1 and also succeeds in receivingdownlink data in unit band 2, the response signal is mapped to PUCCHresources included in PUCCH region 2 and the first constellation pointis used. That is, when there are two downlink unit bands, since thereare four error detection result patterns, the four patterns can berepresented by combinations of two resources and two types ofconstellation point.

CITATION LIST Non-Patent Literature

-   NPL 1-   3GPP TS 36.211 V8.6.0, “Physical Channels and Modulation (Release    8),” March 2009-   NPL 2-   3GPP TS 36.212 V8.6.0, “Multiplexing and channel coding (Release    8),” March 2009-   NPL 3-   3GPP TS 36.213 V8.6.0, “Physical layer procedures (Release 8),”    March 2009-   NPL 4-   Seigo Nakao et al. “Performance enhancement of E-UTRA uplink control    channel in fast fading environments”, Proceeding of VTC2009 spring,    April, 2009-   NPL 5-   ZTE, 3GPP RANI meeting #57, R1-091702, “Uplink Control Channel    Design for LTE-Advanced,” May 2009-   NPL 6-   Panasonic, 3GPP RANI meeting #57, R1-091744, “UL ACK/NACK    transmission on PUCCH for carrier aggregation,” May 2009

SUMMARY OF INVENTION Technical Problem

However, since an arbitrary terminal transmits a response signal usingone of a plurality of PUCCH resources in the aforementioned channelselection, the base station side must secure a plurality of PUCCHresources for the arbitrary terminal.

In an LTE system, since, for example, downlink unit band 1 in FIG. 3B isassociated with uplink unit band 1 to form a band pair and downlink unitband 2 is associated with uplink unit band 2 to form a band pair, PUCCHcorresponding to downlink unit band 2 needs to be provided for onlyuplink unit band 2. On the other hand, in LTE-A, when asymmetric carrieraggregation is individually set (configured) for terminals, as shown inFIG. 3B, uplink unit band 1 also needs to secure PUCCH resources for aresponse signal for downlink unit band 2 caused by the association ofunit bands specific to the LTE-A terminal such as downlink unit band 2and uplink unit band 1. That is, the uplink control channel (PUCCH) ofuplink unit band 1 needs to be provided with an additional region (PUCCHregion 2) in addition to the basic region (PUCCH region 1).

This means that when channel selection is applied as a response signaltransmission method in the LTE-A system, the PUCCH overhead drasticallyincreases compared to the LTE system. This additional overhead for theLTE system increases as the asymmetry between downlink unit bands anduplink unit bands of a terminal increases.

Furthermore, to minimize the aforementioned additional overhead, morePUCCH resources may be secured in PUCCH region 2 than PUCCH region 1(that is, the number of codes multiplexed in the same time/frequencyresource is increased). However, in this case, transmissioncharacteristics of a response signal deteriorate due to influences ofinter-code interference caused by the increase in the number of codesmultiplexed.

It is an object of the present invention to provide a terminal apparatusand retransmission control method for when applying ARQ to communicationusing an uplink unit band and a plurality of downlink unit bandsassociated with the uplink unit band, capable of preventingdeterioration of transmission characteristics of a response signal andsuppressing increases in overhead of an uplink control channel to aminimum.

Solution to Problem

A terminal apparatus according to the present invention is a terminalapparatus that communicates with a base station using a unit band groupmade up of a plurality of downlink unit bands and an uplink unit bandand transmits one bundled response signal through an uplink controlchannel of the uplink unit band based on an error detection result of aplurality of pieces of downlink data arranged in the plurality ofdownlink unit bands, including a downlink data receiving section thatreceives downlink data transmitted through at least one downlink datachannel of the plurality of downlink unit bands, an error detectionsection that detects the presence or absence of a reception error of thereceived downlink data and a response control section that transmits thebundled response signal using one of a first region and a second regionof the uplink control channel based on a reception situation patterndetermined by the error detection result obtained in the error detectionsection, wherein the response control section transmits the bundledresponse signal using resources of the first region in the case of areception situation pattern having a high probability of occurrence andtransmits the bundled response signal using resources of the secondregion in the case of a reception situation pattern having a lowprobability of occurrence.

A retransmission control method according to the present inventionincludes a downlink data receiving step of receiving downlink datatransmitted through at least one downlink data channel of a plurality ofdownlink unit bands included in a unit band group, an error detectionstep of detecting a reception error of the received downlink data and aresponse controlling step of transmitting a bundled response signalusing one of a first region and a second region of an uplink controlchannel in an uplink unit band included in the unit band group based ona reception situation pattern determined by the error detection resultobtained in the error detection step, wherein in the response controlstep, the bundled response signal is transmitted using resources of thefirst region in the case of a reception situation pattern having a highprobability of occurrence and the bundled response signal is transmittedusing resources of the second region in the case of a receptionsituation pattern having a low probability of occurrence.

Advantageous Effects of Invention

The present invention can provide a terminal apparatus andretransmission control method for when applying ARQ to communicationusing an uplink unit band and a plurality of downlink unit bandsassociated with the uplink unit band, capable of preventingdeterioration of transmission characteristics of a response signal andsuppressing increases in overhead of an uplink control channel to aminimum.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a method of spreading a response signaland reference signal;

FIG. 2A and FIG. 2B are diagrams illustrating asymmetric carrieraggregation applied to individual terminals and a control sequencethereof;

FIG. 3A and FIG. 3B are diagrams illustrating ARQ control when carrieraggregation is applied to a terminal;

FIG. 4 is a block diagram showing a configuration of a base stationaccording to Embodiment 1 of the present invention;

FIG. 5 is a block diagram showing a configuration of a terminalaccording to Embodiment 1 of the present invention;

FIG. 6A and FIG. 6B are diagrams illustrating operations of the basestation and terminal;

FIG. 7 is a diagram illustrating operations of the base station andterminal;

FIG. 8 is a diagram illustrating operations of a base station andterminal according to Embodiment 2 of the present invention;

FIG. 9 is a block diagram showing a configuration of a base stationaccording to Embodiment 3 of the present invention;

FIG. 10 is a block diagram showing a configuration of a terminalaccording to Embodiment 3 of the present invention;

FIG. 11 is a diagram illustrating operations of the base station andterminal;

FIG. 12A and FIG. 12B are diagrams illustrating operations of the basestation and terminal; and

FIG. 13 is a diagram illustrating operations of a base station andterminal according to another embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. The same componentsamong different embodiments will be assigned the same reference numeralsand overlapping descriptions thereof will be omitted.

Embodiment 1

[Overview of Communication System]

A communication system including base station 100 and terminal 200,which will be described later, performs communication using an uplinkunit band and a plurality of downlink unit bands associated with theuplink unit band, that is, communication using asymmetric carrieraggregation specific to terminal 200. Furthermore, this communicationsystem also includes terminals that have no capability of performingcommunication using carrier aggregation unlike terminal 200 and performcommunication using one downlink unit band and one uplink unit bandassociated therewith (that is, communication without using carrieraggregation).

Therefore, base station 100 is configured to be able to support bothcommunication using asymmetric carrier aggregation and communicationwithout using carrier aggregation.

Furthermore, communication without using carrier aggregation can also beperformed between base station 100 and terminal 200 depending onresource allocation to terminal 200 by base station 100.

Furthermore, this communication system performs conventional ARQ whenperforming communication without using carrier aggregation on one hand,and adopts channel selection in ARQ when performing communication usingcarrier aggregation on the other. That is, this communication system is,for example, an LTE-A system, base station 100 is, for example, an LTE-Abase station and terminal 200 is, for example, an LTE-A terminal.Furthermore, the terminal having no capability of performingcommunication using carrier aggregation is, for example, an LTEterminal.

Descriptions will be given below assuming the following matters aspremises. That is, asymmetric carrier aggregation specific to terminal200 is configured beforehand between base station 100 and terminal 200and information of downlink unit bands and uplink unit bands to be usedby terminal 200 is shared between base station 100 and terminal 200.Furthermore, the downlink unit band set (configured) for arbitraryterminal 200 by base station 100 for transmitting BCH for broadcastinginformation on an uplink unit band making up a unit band group reported(signaled) to terminal 200 beforehand is a “base unit band” for terminal200. The information on this base unit band is “base unit bandinformation.” Therefore, arbitrary terminal 200 can recognize the baseunit band information by reading BCH information in each downlink unitband.

[Configuration of Base Station]

FIG. 4 is a block diagram showing a configuration of base station 100according to Embodiment 1 of the present invention. In FIG. 4, basestation 100 includes control section 101, control information generationsection 102, coding section 103, modulation section 104, broadcastsignal generation section 105, coding section 106, data transmissioncontrol section 107, modulation section 108, mapping section 109, IFFTsection 110, CP adding section 111, radio transmitting section 112,radio receiving section 113, CP removing section 114, PUCCH extractionsection 115, despreading section 116, sequence control section 117,correlation processing section 118, decision section 119 andretransmission control signal generation section 120.

Control section 101 allocates (assigns), to resource allocation targetterminal 200, downlink resources to transmit control information (thatis, downlink control information allocation resources), downlinkresources to transmit downlink data included in the control information(that is, downlink data allocation resources). Such resources areallocated in downlink unit bands included in a unit band group set inresource allocation target terminal 200. Furthermore, the downlinkcontrol information allocation resources are selected from amongresources corresponding to a downlink control channel (PDCCH) in eachdownlink unit band. Furthermore, the downlink data allocation resourcesare selected from among resources corresponding to a downlink datachannel (PDSCH) in each downlink unit band. Furthermore, when there area plurality of resource allocation target terminals 200, control section101 allocates different resources to respective resource allocationtarget terminals 200.

The downlink control information allocation resources are equivalent toabove-described L1/L2 CCHs. That is, each of the downlink controlinformation allocation resources is made up of one or a plurality ofCCEs. Furthermore, each CCE in the base unit band is associated with acomponent resource in an uplink control channel region (PUCCH region) inan uplink unit band in the unit band group in a one-to-onecorrespondence.

Furthermore, control section 101 determines a coding rate used totransmit control information to resource allocation target terminal 200.Since the amount of data of the control information differs according tothis coding rate, control section 101 allocates downlink controlinformation allocation resources having a number of CCEs to whichcontrol information corresponding to this amount of data is mapped.

Furthermore, control section 101 generates a DAI (Downlink AssignmentIndicator) which is information indicating which downlink unit band isused to allocate downlink resources to resource allocation targetterminal 200.

Control section 101 then outputs information on the downlink dataallocation resources and a DAI to control information generation section102. Furthermore, control section 101 outputs information on a codingrate to coding section 103. Furthermore, control section 101 determinesa coding rate of transmission data (that is, downlink data) and outputsthe coding rate to coding section 106. Furthermore, control section 101outputs information on the downlink data allocation resources anddownlink control information allocation resources to mapping section109. However, control section 101 performs control so as to map downlinkdata and downlink control information for the downlink data to the samedownlink unit band.

Furthermore, control section 101 outputs information on the maximumnumber of code-multiplexed PUCCH signals per unit time/frequencyresource (1 resources block: 1 RB) (that is, multiplexing levelinformation) arranged in each PUCCH region to broadcast signalgeneration section 105. Furthermore, control section 101 outputs acontrol signal to generate a broadcast channel signal (BCH) to betransmitted to broadcast signal generation section 105. Control over thenumber of PUCCH resources per unit time/frequency resource in each PUCCHregion will be described in detail later.

Control information generation section 102 generates information ondownlink data allocation resources and control information including aDAI and outputs the information to coding section 103. The controlinformation is generated for each downlink unit band. Furthermore, whenthere are a plurality of resource allocation target terminals 200, thecontrol information includes a terminal ID of a destination terminal todistinguish between resource allocation target terminals 200. Forexample, the control information includes a CRC bit masked with aterminal ID of the destination terminal. This control information may becalled “downlink allocation control information.” Furthermore, the DAIis included in all control information directed to resource allocationtarget terminals 200.

Coding section 103 codes control information according to the codingrate received from control section 101 and outputs the coded controlinformation to modulation section 104.

Modulation section 104 modulates the coded control information andoutputs the modulated signal obtained to mapping section 109.

Broadcast signal generation section 105 generates a broadcast signal(BCH) for each downlink unit band according to the information andcontrol signal received from control section 101 and outputs thebroadcast signal to mapping section 109.

Coding section 106 receives transmission data per destination terminal200 (that is, downlink data) and coding rate information from controlsection 101 as input, codes transmission data and outputs the codedtransmission data to data transmission control section 107. However,when a plurality of downlink unit bands are allocated to destinationterminal 200, transmission data transmitted in each downlink unit bandis coded and the coded transmission data is outputted to datatransmission control section 107.

Upon initial transmission, data transmission control section 107 storesthe coded transmission data and also outputs the coded transmission datato modulation section 108. The coded transmission data is stored foreach destination terminal 200. Furthermore, transmission data for onedestination terminal 200 is stored for each downlink unit bandtransmitted. This enables not only retransmission control over theentire data transmitted to destination terminal 200 but alsoretransmission control over each downlink unit band.

Furthermore, upon receiving NACK or DTX for downlink data transmitted ina certain downlink unit band from retransmission control signalgeneration section 120, data transmission control section 107 outputsthe stored data corresponding to this downlink unit band to modulationsection 108. Upon receiving ACK for downlink data transmitted in acertain downlink unit band from retransmission control signal generationsection 120, data transmission control section 107 deletes the storeddata corresponding to this downlink unit band.

Modulation section 108 modulates the coded transmission data receivedfrom data transmission control section 107 and outputs the modulatedsignal to mapping section 109.

Mapping section 109 maps the modulated signal of the control informationreceived from modulation section 104 to resources indicated by thedownlink control information allocation resources received from controlsection 101 and outputs the mapping result to IFFT section 110.

Furthermore, mapping section 109 maps the modulated signal of thetransmission data received from modulation section 108 to resourcesindicated by the downlink data allocation resources received fromcontrol section 101 and outputs the mapping result to IFFT section 110.

Mapping section 109 maps broadcast information to predeterminedtime/frequency resources and outputs the mapped broadcast information toIFFT section 110.

The control information, transmission data or broadcast signal mapped bymapping section 109 to a plurality of subcarriers in a plurality ofdownlink unit bands is transformed by IFFT section 110 from a frequencydomain signal into a time domain signal, transformed into an OFDM signalwith a CP added by CP adding section 111, subjected to transmissionprocessing such as D/A conversion, amplification and up-conversion inradio transmitting section 112 and transmitted to terminal 200 via anantenna.

Radio receiving section 113 receives a response signal or referencesignal transmitted from terminal 200 via the antenna and performsreception processing such as down-conversion and A/D conversion on theresponse signal or reference signal.

CP removing section 114 removes a CP added to the response signal orreference signal after the reception processing.

PUCCH extraction section 115 extracts an uplink control channel signalincluded in the received signal for each PUCCH region and distributesthe extracted signals. This uplink control channel signal may include aresponse signal and a reference signal transmitted from terminal 200.

Despreading section 116-N, correlation processing section 118-N anddecision section 119-N perform processing on the uplink control channelsignal extracted in PUCCH region N. Base station 100 is provided withprocessing systems of despreading section 116, correlation processingsection 118 and decision section 119 corresponding to respective PUCCHregions 1 to N used by base station 100.

To be more specific, despreading section 116 despreads a signalcorresponding to a response signal with an orthogonal code sequence forterminal 200 to use for secondary-spreading in the respective PUCCHregions and outputs the despread signal to correlation processingsection 118. Furthermore, despreading section 116 despreads a signalcorresponding to the reference signal with an orthogonal code sequencefor terminal 200 to use to spread the reference signal in the respectiveuplink unit bands and outputs the despread signal to correlationprocessing section 118.

Sequence control section 117 generates a ZAC sequence that may bepossibly used to spread a response signal and reference signaltransmitted from terminal 200. Furthermore, sequence control section 117identifies a correlation window in which signal components from terminal200 should be included in PUCCH regions 1 to N respectively based oncode resources (e.g., amount of cyclic shift) that may be possibly usedby terminal 200. Sequence control section 117 then outputs theinformation indicating the identified correlation window and thegenerated ZAC sequence to correlation processing section 118.

Correlation processing section 118 calculates a correlation valuebetween the signal inputted from despreading section 116 and the ZACsequence that may be possibly used for primary spreading in terminal 200using information indicating the correlation window inputted fromsequence control section 117 and the ZAC sequence and outputs thecorrelation value to decision section 119.

Decision section 119 decides whether the response signal transmittedfrom the terminal indicates ACK or NACK, or DTX with respect to the datatransmitted in their respective downlink unit bands based on thecorrelation value inputted from correlation processing section 118. Thatis, decision section 119 decides, when the magnitude of the correlationvalue inputted from correlation processing section 118 is a threshold orbelow, that terminal 200 is transmitting neither ACK nor NACK using theresources, and further decides, when the magnitude of the correlationvalue is the threshold or above, which constellation point the responsesignal indicates through coherent detection. Decision section 119 thenoutputs the decision result in each PUCCH region to retransmissioncontrol signal generation section 120.

Retransmission control signal generation section 120 decides whether ornot to retransmit the data transmitted in each downlink unit band basedon the information inputted from decision section 119 and generates aretransmission control signal based on the decision result.

That is, retransmission control signal generation section 120 initiallydecides in which PUCCH region corresponding to decision sections 119-1to N a maximum correlation value is detected. Next, retransmissioncontrol signal generation section 120 individually generates an ACKsignal or NACK signal for the data transmitted in each downlink unitband depending on which constellation point the response signaltransmitted in the PUCCH region where the maximum correlation value isdetected and outputs the ACK signal or NACK signal to data transmissioncontrol section 107. However, when all correlation values detected ineach PUCCH region are equal to or below a threshold, retransmissioncontrol signal generation section 120 decides that no response signal istransmitted from terminal 200, generates DTX for all downlink data andoutputs the DTX to data transmission control section 107.

Details of the processing of decision section 119 and retransmissioncontrol signal generation section 120 will be described later.

[Configuration of Terminal]

FIG. 5 is a block diagram showing a configuration of terminal 200according to Embodiment 1 of the present invention. In FIG. 5, terminal200 includes radio receiving section 201, CP removing section 202, FFTsection 203, extraction section 204, broadcast signal receiving section205, demodulation section 206, decoding section 207, decision section208, control section 209, demodulation section 210, decoding section211, CRC section 212, response signal generation section 213, modulationsection 214, primary-spreading section 215, secondary-spreading section216, IFFT section 217, CP adding section 218 and radio transmittingsection 219.

Radio receiving section 201 receives an OFDM signal transmitted frombase station 100 via an antenna and performs reception processing suchas down-conversion, A/D conversion on the received OFDM signal.

CP removing section 202 removes a CP added to the OFDM signal after thereception processing.

FFT section 203 applies FFT to the received OFDM signal, transforms theOFDM signal into a frequency domain signal and outputs the receivedsignal obtained to extraction section 204.

Extraction section 204 extracts a broadcast signal from the receivedsignal received from FFT section 203 and outputs the broadcast signal tobroadcast signal receiving section 205. Since resources to which thebroadcast signal is mapped are predetermined, extraction section 204extracts information mapped to the resources. Furthermore, the extractedbroadcast signal includes information on the association between eachdownlink unit band and uplink unit band and information on the number ofPUCCH resources included in each PUCCH region.

Furthermore, extraction section 204 extracts a downlink control channelsignal (PDCCH signal) from the received signal received from FFT section203 according to the inputted coding rate information. That is, sincethe number of CCEs making up downlink control information allocationresources changes according to the coding rate, extraction section 204extracts a downlink control channel signal using a number of CCEscorresponding to the coding rate as an extraction unit. Furthermore, thedownlink control channel signal is extracted for each downlink unitband. The extracted downlink control channel signal is outputted todemodulation section 206.

Furthermore, extraction section 204 extracts downlink data from thereceived signal based on the information on the downlink data allocationresources directed to the terminal received from decision section 208and outputs the downlink data to demodulation section 210.

Broadcast signal receiving section 205 decodes each broadcast signalincluded in each downlink unit band and extracts information of anuplink unit band forming a pair with each downlink unit band (that is,information of the uplink unit band reported by SIB2 mapped to eachdownlink unit band). Furthermore, broadcast signal receiving section 205recognizes the downlink unit band that forms a pair with the uplink unitband included in the unit band group directed to the terminal as a “baseunit band” and outputs the base unit band information to decisionsection 208 and control section 209.

Furthermore, broadcast signal receiving section 205 extracts informationon the number of codes multiplexed in each PUCCH region provided incorrespondence with each downlink unit band (that is, information on thenumber of PUCCH resources per unit time/frequency resource defined ineach PUCCH region (multiplexing level information)) and outputs theinformation to control section 209.

Demodulation section 206 demodulates the downlink control channel signalreceived from extraction section 204 and outputs the demodulation resultobtained to decoding section 207.

Decoding section 207 decodes the demodulation result received fromdemodulation section 206 according to the coding rate informationinputted and outputs the decoding result obtained to decision section208.

Decision section 208 makes a blind decision as to whether or not thecontrol information included in the decoding result received fromdecoding section 207 is control information directed to the terminal.This decision is made based on the unit of the decoding result withrespect to the above-described extraction unit. For example, decisionsection 208 demasks the CRC bit with the terminal ID of the terminal anddecides that control information with CRC=OK (no error) is controlinformation directed to the terminal. Decision section 208 then outputsinformation on the downlink data allocation resources for the terminalincluded in the control information directed to the terminal toextraction section 204. Furthermore, decision section 208 outputs a DAIincluded in the control information directed to the terminal to controlsection 209.

Furthermore, decision section 208 identifies a CCE to which theabove-described control information directed to the terminal is mappedon the downlink control channel of the base unit band and outputsidentification information of the identified CCE to control section 209.

Control section 209 identifies PUCCH resources (frequency/code)corresponding to the CCE indicated by the CCE identification informationreceived from decision section 208. That is, control section 209identifies PUCCH resources in the basic region of the uplink controlchannel (that is, “basic PUCCH resources”) based on the CCEidentification information. However, control section 209 storesinformation on the PUCCH resources in an additional region for channelselection reported from base station 100 to terminal 200 (that is,“additional PUCCH resources”).

Control section 209 determines which of the basic PUCCH resource oradditional PUCCH resource is used to transmit a response signal based onthe situation of success/failure in reception of the downlink data ineach downlink unit band inputted from CRC section 212. That is, controlsection 209 determines which of the basic PUCCH resource or additionalPUCCH resource is used to transmit a response signal according to apattern of error detection results regarding a plurality of pieces ofdownlink data. Furthermore, control section 209 determines whichconstellation point is set for the response signal based on thesituation of success/failure in reception of downlink data in eachdownlink unit band inputted from CRC section 212.

Control section 209 then outputs information on the constellation pointto be set to response signal generation section 213, outputs the ZACsequence and amount of cyclic shift corresponding to the PUCCH resourcesto be used to primary-spreading section 215 and outputs frequencyresource information to IFFT section 217. Furthermore, control section209 outputs an orthogonal code sequence corresponding to the PUCCHresources to be used to secondary-spreading section 216. Details ofcontrol over PUCCH resources and constellation points by control section209 will be described later.

Demodulation section 210 demodulates the downlink data received fromextraction section 204 and outputs the demodulated downlink data todecoding section 211.

Decoding section 211 decodes the downlink data received fromdemodulation section 210 and outputs the decoded downlink data to CRCsection 212.

CRC section 212 generates the decoded downlink data received fromdecoding section 211, performs error detection for each downlink unitband using a CRC and outputs ACK when CRC=OK (no error) and NACK whenCRC=NG (error present) to control section 209. Furthermore, when CRC=OK(no error), CRC section 212 outputs the decoded downlink data as thereceived data.

Response signal generation section 213 generates a response signal andreference signal based on the constellation points of the responsesignal instructed from control section 209 and outputs the responsesignal and reference signal to modulation section 214.

Modulation section 214 modulates the response signal inputted fromresponse signal generation section 213 and outputs the modulatedresponse signal to primary-spreading section 215.

Primary-spreading section 215 primary-spreads the response signal andreference signal based on the ZAC sequence and amount of cyclic shiftset by control section 209 and outputs the primary-spread responsesignal and reference signal to secondary-spreading section 216. That is,primary-spreading section 215 primary-spreads the response signal andreference signal according to the instruction from control section 209.

Secondary-spreading section 216 secondary-spreads the response signaland reference signal using an orthogonal code sequence set by controlsection 209 and outputs the secondary-spread signal to IFFT section 217.That is, secondary-spreading section 216 secondary-spreads theprimary-spread response signal and reference signal using an orthogonalcode sequence corresponding to the PUCCH resources selected by controlsection 209 and outputs the spread signal to IFFT section 217.

CP adding section 218 adds the same signal as that of the rear part ofthe signal after the IFFT at the head of the signal as a CP.

Radio transmitting section 219 performs transmission processing such asD/A conversion, amplification and up-conversion on the signal inputted.Radio transmitting section 219 then transmits the signal to base station100 from the antenna.

[Operations of Base Station 100 and Terminal 200]

Operations of base station 100 and terminal 200 having theabove-described configurations will be described. FIG. 6A, FIG. 6B andFIG. 7 are diagrams illustrating operations of base station 100 andterminal 200.

<Control by Base Station 100 Over PUCCH Multiplexing Level in UnitTime/Frequency Resources>

In base station 100, control section 101 sets the multiplexing level ofa PUCCH signal in each PUCCH region independently of each other.

For example, in FIG. 7, 18 PUCCH resources #1 to 18 per unittime/frequency resource are defined in PUCCH region 1 (that is, regionwhere a response signal from an LTE terminal and a response signal froman LTE-A terminal coexist). On the other hand, 36 PUCCH resources #1 to36 per unit time/frequency resource are defined in PUCCH region 2 (thatis, additional PUCCH region reported to LTE-A terminal). Basic PUCCHresources directed to terminal 200 are included in PUCCH region 1 andadditional PUCCH resources directed to terminal 200 are included inPUCCH region 2.

Thus, base station 100 sets a multiplexing level per unit time/frequencyresource in each PUCCH region independently of each other. To be morespecific, this multiplexing level is identified by the number ofpositions out of positions that can be taken as a cyclic shift index. Tobe more specific, the multiplexing level is identified based on theinterval at which positions are used. In FIG. 7, 12 positions can betaken for one sequence. A sequence corresponding to every one cyclicshift index is used in PUCCH region 1, while a cyclic shift sequencecorresponding to all 12 cyclic shift indices is used in PUCCH region 2.That is, positions are used at 0 intervals in PUCCH region 2. Therefore,in FIG. 7, 18 PUCCH resources are provided in PUCCH region 1, while 36PUCCH resources are provided in PUCCH region 2. That is, more boxes(that is, PUCCH resources) are provided for accommodating PUCCH signalsin PUCCH region 2 than in PUCCH region 1.

Furthermore, PUCCH resources in PUCCH region 1 are associated with CCEsin the respective base unit bands in a one-to-one correspondence andinformation on this association is shared between base station 100 andterminal 200 beforehand.

<Reception of Downlink Data by Terminal 200>

In terminal 200, broadcast signal receiving section 205 identifies adownlink unit band to transmit a BCH for broadcasting information on theuplink unit band making up the unit band group reported to terminal 200as a base unit band.

Furthermore, decision section 208 decides whether or not downlinkallocation control information directed to the terminal is included in adownlink control channel of each downlink unit band and outputs thedownlink allocation control information directed to the terminal toextraction section 204.

Extraction section 204 extracts downlink data from the received signalbased on the downlink allocation control information received fromdecision section 208.

Thus, terminal 200 can receive downlink data transmitted from basestation 100.

Explaining more specifically with reference to FIG. 6A, since a BCH forbroadcasting information on uplink unit band 1 is transmitted indownlink unit band 1 first, downlink unit band 1 becomes the base unitband of terminal 200.

Furthermore, the downlink allocation control information transmitted indownlink unit band 1 includes information on resources used to transmitdownlink data (DL data) transmitted in downlink unit band 1 and thedownlink allocation control information transmitted in downlink unitband 2 includes information on resources used to transmit downlink datatransmitted in downlink unit band 2.

Therefore, by receiving the downlink allocation control informationtransmitted in downlink unit band 1 and the downlink allocation controlinformation transmitted in downlink unit band 2, terminal 200 canreceive downlink data in both downlink unit band 1 and downlink unitband 2. On the contrary, when the terminal cannot receive downlinkallocation control information in a certain downlink unit band, terminal200 cannot receive downlink data in the downlink unit band.

Furthermore, terminal 200 can recognize the downlink unit band in whichdownlink allocation control information is transmitted through a DAItransmitted in each downlink unit band.

<Response by Terminal 200>

CRC section 212 performs error detection on downlink data correspondingto the downlink allocation control information that has beensuccessfully received and outputs the error detection result to controlsection 209.

Control section 209 then performs transmission control over a responsesignal based on the error detection result received from CRC section 212as follows.

That is, as shown in FIG. 6B, when both the error detection resultregarding the downlink data transmitted in the base unit band and theerror detection result regarding the downlink data transmitted in otherthan the base unit band are “no error” (that is, ACK/ACK), controlsection 209 transmits a response signal using basic PUCCH resources(that is, resources of PUCCH region 1). A first constellation point(e.g., (I,Q)=(1,0) or the like) is used for the response signal in thiscase. Furthermore, as described above, the basic PUCCH resources aredetermined in association with CCEs occupied by the downlink allocationcontrol information transmitted to terminal 200 in the base unit band.

Furthermore, when both the error detection result regarding the downlinkdata transmitted in the base unit band and the error detection resultregarding the downlink data transmitted in other than the base unit bandare “error present” (that is, NACK/NACK), control section 209 transmitsa response signal using additional PUCCH resources (that is, resourcesof PUCCH region 2). A second constellation point (e.g., (I,Q)=(−1,0) orthe like) is used for the response signal in this case. The informationof additional PUCCH resources is shared between base station 100 andterminal 200 beforehand as described above.

Furthermore, when the downlink data transmitted in the base unit band is“no error” and the downlink data transmitted in other than the base unitband is “error present” (that is, ACK/NACK), control section 209transmits a response signal using the basic PUCCH resources. A secondconstellation point (that is, (I,Q)=(−1,0) or the like) is used for theresponse signal in this case.

Furthermore, when the downlink data transmitted in the base unit band is“error present” and the downlink data transmitted in other than the baseunit band is “no error” (that is, NACK/ACK), control section 209transmits a response signal using additional PUCCH resources. A firstconstellation point (that is, (I,Q)=(1,0) or the like) is used for theresponse signal in this case.

Thus, response signals corresponding to two error detection resultpatterns are mapped to the basic PUCCH resources and additional PUCCHresources respectively. Therefore, BPSK having two constellation pointsis used.

When the terminal receives downlink allocation control signals in someof the plurality of downlink unit bands and although the terminalrecognizes that downlink data is allocated in other downlink unit bandsthrough a DAI included therein, the terminal fails to receive thedownlink allocation control signals in the other downlink unit bands andcannot thereby receive downlink data (that is, a DTX occurs in the otherdownlink unit bands), this case is treated in the same way as in a casewith “error present” in the downlink unit band where the terminal failsto receive the downlink allocation control signal.

Here, the base station generally controls the coding rate and modulationscheme of downlink data so that the assumed error rate (Target BlockError Rate: Target BLER) of downlink data is on the order of 0% to 30%(operation assuming the error rate to be on the order of 10% is mosttypical). Thus, the possibility that the error detection result withrespect to downlink data may be “no error” on the terminal side ishigher than the possibility that the error detection result may be“error present.” That is, as shown in FIG. 6B, when there are twodownlink unit bands included in the unit band group, the probabilitythat errors may be detected in none of downlink data transmitted in therespective downlink unit bands is approximately 81%, while theprobability that errors may be detected in both of downlink data isapproximately 1%.

Therefore, it is possible to suppress the frequency with which theadditional region is used to a low level by transmitting a bundledresponse signal (that is, response signal where resources andconstellation points to be used are determined through operation ofChannel Selection) using resources in the basic region associated withthe downlink control channel of the base unit band when errors aredetected in none of the plurality of pieces of downlink data transmittedin a plurality of downlink unit bands included in the unit band group ortransmitting a bundled response signal using resources in the additionalregion when errors are detected in all pieces of downlink data.Moreover, even when the multiplexing level in unit time/frequencyresources included in the additional region is increased to minimizeincreases in overhead due to the additional region, the frequency withwhich the bundled response signal is mapped to the additional region issuppressed to a low level, and increases in inter-code interference arealso thereby suppressed.

Thus, it is possible to prevent deterioration of transmissioncharacteristics of a response signal and also minimize increases inoverhead to the uplink control channel.

That is, in the LTE-A system, even when the maximum allowable number ofcodes multiplexed is increased to drastically reduce the number oftime/frequency resources occupied by the PUCCH region (that is, PUCCHregion 2) additionally required for the LTE system, it is possible toreduce the influence of inter-code interference caused by an increase inthe maximum allowable number of codes multiplexed by reducing theprobability that additional PUCCH resources may be used (that is,control of channel selection is performed whereby basic PUCCH resourcesare used when all downlink data shows “no error” or additional PUCCHresources are used when all downlink data shows “error present”).

As described above, according to the present embodiment, control section209 in terminal 200 transmits a bundled response signal using resourcesin the basic region of the uplink control channel in the uplink unitband associated with the downlink control channel of the base unit bandwhich is the downlink unit band for transmitting a broadcast channelsignal including information on the uplink unit band of the unit bandgroup when errors are detected in none of the plurality of pieces ofdownlink data of the unit band group or transmits a bundled responsesignal using resources in the additional region of the uplink controlchannel when errors are detected in all of the plurality of pieces ofdownlink data.

By so doing, it is possible to reduce the frequency with which thebundled response signal is mapped to the additional region compared tothe basic region. Since the frequency with which the bundled responsesignal is mapped to the additional region can be suppressed to a lowlevel, it is possible to prevent inter-code interference fromincreasing, at the same time increase the multiplexing level of theadditional region and minimize increases in overhead due to theadditional region.

A case has been described above assuming that information on theadditional PUCCH resources is shared beforehand between base station 100and terminal 200. That is, it is assumed that information on theadditional PUCCH resources is explicitly reported from base station 100to terminal 200. However, the present invention is not limited to this,but additional PUCCH resources as well as basic PUCCH resources may alsobe defined in association with CCEs occupied by downlink allocationcontrol information transmitted in other than the base unit band (thatis, implicit additional PUCCH resource signaling may be applied). By sodoing, it is possible to reduce signaling overhead regarding theadditional PUCCH resources.

Furthermore, when additional PUCCH resources are associated with CCEsoccupied by downlink allocation control information transmitted in otherthan the base unit band, a plurality of CCEs (e.g. m continuous CCEs) inother than the base unit band may be associated with one additionalPUCCH resource to reduce the number of additional PUCCH resources. By sodoing, the number of additional PUCCH resources to be defined in theadditional region of the uplink control channel is reduced to the numberof CCEs/m, and therefore PUCCH overhead is further reduced.

The above explanation presupposes that the basic region including basicPUCCH resources does not overlap with the additional region includingadditional PUCCH resources. However, the present invention is notlimited to this, but the basic region may partially or totally overlapwith the additional region. In short, the base station side needs onlyto perform control such that the basic PUCCH resources and additionalPUCCH resources that should be recognized by a certain terminal in acertain subframe are different from each other. Base station 100provides the basic region and additional region overlapping with eachother in this way, and PUCCH overhead in the present system is therebyreduced to the equivalent of that of an LTE system.

A case has been described above where a ZAC sequence is used forprimary-spreading and an orthogonal code sequence is used forsecondary-spreading. However, the present invention may also use non-ZACsequences which are mutually separable by different cyclic shift indicesfor primary-spreading. For example, GCL (Generalized Chirp like)sequence, CAZAC (Constant Amplitude Zero Auto Correlation) sequence, ZC(Zadoff-Chu) sequence, M sequence, PN sequence such as orthogonal goldcode sequence or a sequence randomly generated by a computer and havingan abrupt auto-correlation characteristic on the time axis or the likemay be used for primary-spreading. Furthermore, sequences orthogonal toeach other or any sequences may be used as orthogonal code sequences forsecondary-spreading as long as they are regarded as sequencessubstantially orthogonal to each other. For example, a Walsh sequence orFourier sequence or the like may be used for secondary-spreading as anorthogonal code sequence. In the above descriptions, resources (e.g.,PUCCH resources) of response signals are defined by a cyclic shift indexof a ZAC sequence and a sequence number of an orthogonal cover index.

Embodiment 2

A case has been described in Embodiment 1 assuming that when theterminal generates a response signal, a case of failing to receivedownlink data is treated the same as a case of failing to receive adownlink allocation control signal. In Embodiment 2, when the terminalgenerates a response signal, a case of failing to receive downlink datais distinguished from a case of failing to receive a downlink allocationcontrol signal. In Embodiment 2, this allows the base station side todistinguish whether the terminal fails to receive downlink data in eachunit band or fails to receive a downlink allocation control signal, thusenabling more effective retransmission control.

This will be described more specifically below. Since the configurationsof the base station and terminal according to Embodiment 2 are similarto those of Embodiment 1, the present embodiment will be described usingFIG. 4 and FIG. 5.

In terminal 200 according to Embodiment 2, control section 209determines which of basic PUCCH resources or additional PUCCH resourcesare used to transmit a response signal according to a pattern ofsuccess/failure in reception of a plurality of downlink allocationcontrol signals and a pattern of error detection results of a pluralityof pieces of downlink data.

To be more specific, control section 209 performs the followingtransmission control over a response signal based on a pattern ofsuccess/failure in reception of a plurality of downlink allocationcontrol signals and a pattern of error detection results of a pluralityof pieces of downlink data.

That is, when control section 209 receives downlink allocation controlinformation in a base unit band and downlink unit bands other than thebase unit band, if all error detection results regarding downlink datatransmitted in the base unit band and downlink data transmitted in otherthan the base unit band show “no error,” control section 209 transmits aresponse signal using basic PUCCH resources. A first constellation point(e.g., (I,Q)=(1,0) or the like) is used for the response signal in thiscase. Furthermore, as described above, basic PUCCH resources aredetermined in association with CCEs occupied by the downlink allocationcontrol information transmitted to terminal 200 in the base unit band.

Furthermore, when control section 209 receives downlink allocationcontrol information in the base unit band and other downlink unit bands,if downlink data transmitted in the base unit band shows “no error” anddownlink data transmitted in other than the base unit band shows “errorpresent,” control section 209 transmits a response signal using basicPUCCH resources. A second constellation point (that is, (I,Q)=(−1,0) orthe like) is used for the response signal in this case.

Furthermore, when control section 209 receives downlink allocationcontrol information in the base unit band and other downlink unit bands,if downlink data transmitted in the base unit band shows “error present”and downlink data transmitted in other than the base unit band shows “noerror,” control section 209 transmits a response signal using basicPUCCH resources. A third constellation point (that is, (I,Q)=(0,j) orthe like) is used for the response signal in this case.

Furthermore, when control section 209 receives downlink allocationcontrol information in the base unit band and other downlink unit bands,if both downlink data transmitted in the base unit band and downlinkdata transmitted in other than the base unit band show “error present,”control section 209 transmits a response signal using basic PUCCHresources. A fourth constellation point (that is, (I,Q)=(0,−j) or thelike) is used for the response signal in this case.

Furthermore, when control section 209 receives downlink allocationcontrol information in only one of the base unit band and downlink unitbands other than the base unit band, if a DAI included in the downlinkallocation control information indicates that downlink data is presentin both the base unit band and downlink unit bands other than the baseunit band, control section 209 transmits a response signal usingadditional PUCCH resources. That is, when DTX occurs, control section209 transmits a response signal using additional PUCCH resources.However, since the information on the additional PUCCH resources isshared beforehand between base station 100 and terminal 200 as describedabove, terminal 200 can reliably grasp additional PUCCH resources to beused even when it fails to receive downlink allocation controlinformation in the base unit band.

When control section 209 receives downlink allocation controlinformation in only downlink unit bands other than the base unit band,if error detection results regarding the downlink data transmitted inthe other downlink unit bands show “no error,” control section 209 usesa first constellation point (that is, (I,Q)=(1,0) or the like) as theresponse signal.

Furthermore, when control section 209 receives downlink allocationcontrol information in only downlink unit bands other than the base unitband, if error detection results regarding the downlink data transmittedin the other downlink unit bands show “error present,” control section209 uses a second constellation point (that is, (I,Q)=(−1,0) or thelike) as the response signal.

Furthermore, when control section 209 receives downlink allocationcontrol information in only the base unit band, if error detectionresults regarding the downlink data transmitted in the base unit bandshow “no error,” control section 209 uses a third constellation point(that is, (I,Q)=(0,j) or the like) as the response signal.

Furthermore, when control section 209 receives downlink allocationcontrol information in only the base unit band, if error detectionresults regarding the downlink data transmitted in the base unit bandshow “error present,” control section 209 uses a fourth constellationpoint (that is, (I,Q)=(0,−j) or the like) as the response signal.

Thus, response signals corresponding to four patterns of success/failurein reception of downlink allocation control information and errordetection results are mapped to the basic PUCCH resources and additionalPUCCH resources respectively. Therefore, QPSK having four constellationpoints is used.

Here, the base station generally controls the coding rate and modulationscheme of downlink allocation control information so that the assumederror rate of the downlink allocation control information is on theorder of 0% to 1%. That is, the probability that the terminal side mayfail to receive downlink allocation control information, that is, theprobability that DTX may occur is very low. That is, as shown in FIG. 8,the probability that DTX may occur is approximately 2% at most even whenprobabilities of all four patterns are summed up.

Therefore, by transmitting a bundled response signal using resources inthe additional region only when DTX occurs, it is possible to furthersuppress the frequency with which the additional region is used to alower level than Embodiment 1. This makes it possible to furthersuppress increases in overhead of the uplink channel while suppressingincreases in inter-code interference.

Embodiment 3

Cases have been described in Embodiments 1 and 2 where the base stationtransmits downlink allocation control information including information(that is, DAI) as to whether or not downlink data is transmitted in adownlink unit band to the terminal, but Embodiment 3 is different fromEmbodiments 1 and 2 in that the base station transmits no DAI.

Furthermore, in Embodiment 3, the base station sets one of a pluralityof downlink unit bands set in the terminal as a “preferential downlinkunit band” (may be referred to as “Primary Component carrier” or “AnchorCarrier”) in the terminal. However, the preferential downlink unit bandmay also be set as the downlink unit band used for terminal 400 toestablish communication shown in FIG. 2A (that is, downlink unit bandused for Initial Access process before performing carrier aggregationcommunication). Alternatively, the preferential downlink unit band maybe individually reported (Dedicated signaling) to terminal 400 from basestation 300 independently of Initial Access process. This preferentialdownlink unit band is a downlink unit band preferentially used whenthere is only one piece of downlink data from the base station to theterminal (that is, when the base station does not require communicationusing carrier aggregation) and the preferential downlink unit band has ahigher probability that it may be used to transmit downlink data thanother downlink unit bands (Non-Primary Component carrier or Non-AnchorCarrier).

[Overview of Communication System]

In the communication system including base station 300 and terminal 400,which will be described later, communication using an uplink unit bandand a plurality of downlink unit bands associated with the uplink unitband, that is, communication using asymmetric carrier aggregationspecific to terminal 400 is performed. Furthermore, as in the cases ofEmbodiments 1 and 2, this communication system also includes terminals,unlike terminal 400, that has no capability to perform communicationusing carrier aggregation and performs communication using one downlinkunit band and one uplink unit band associated therewith (that is,communication without using carrier aggregation).

Therefore, base station 300 is configured to be able to support bothcommunication using asymmetric carrier aggregation and communicationwithout using carrier aggregation.

Furthermore, communication without using carrier aggregation can also beperformed between base station 300 and terminal 400 depending onresource allocation by base station 300 to terminal 400. However, whenperforming communication without using carrier aggregation with terminal400, base station 300 uses only one “preferential downlink unit band”set beforehand in terminal 400.

Furthermore, this communication system adopts channel selection in ARQregardless of whether or not communication using carrier aggregation isperformed. That is, when downlink data is transmitted without using someof the plurality of downlink unit bands set by base station 300beforehand in terminal 400, the terminal 400 side sets feedback on thesome unused downlink unit bands as DTX and performs channel selectionoperation. However, when terminal 400 cannot detect even one piece ofdownlink allocation control information (and downlink data), terminal400 transmits no response signal.

Descriptions will be given below assuming the following matters aspremises. That is, asymmetric carrier aggregation specific to terminal400 is configured beforehand between base station 300 and terminal 400and information of the downlink unit band and uplink unit band forterminal 400 to use is shared between base station 300 and terminal 400.Furthermore, base station 300 reports information on a “preferentialdownlink unit band” to terminal 400 beforehand.

[Configuration of Base Station]

Control section 301 of base station 300 shown in FIG. 9 allocates(assigns), as in the case of Embodiments 1 and 2, downlink resources totransmit control information (that is, downlink control informationallocation resources) and downlink resources to transmit downlink dataincluded in the control information (that is, downlink data allocationresources) to resource allocation target terminal 400.

Furthermore, control section 301 controls terminal 400 so as to usecommunication without using carrier aggregation (that is, when thenumber of downlink unit bands for allocating downlink data to terminal400 is only one) and “preferential downlink unit band” for terminal 400.However, unlike Embodiments 1 and 2, control section 301 does notgenerate DAI information for resource allocation target terminal 400.

Control section 301 then outputs information on downlink data allocationresources to control information generation section 302.

Upon initial transmission, data transmission control section 307 storesthe coded transmission data and also outputs the coded transmission datato modulation section 108. The coded transmission data is stored foreach destination terminal 400. Furthermore, transmission data for onedestination terminal 400 is stored for each downlink unit bandtransmitted.

This enables not only retransmission control over the entire datatransmitted to destination terminal 400 but also retransmission controlover each downlink unit band.

Furthermore, data transmission control section 307 receives NACK fordownlink data transmitted in a certain downlink unit band or DTX for thedownlink unit band from retransmission control signal generation section120 and outputs, if the downlink data was actually transmitted in thedownlink unit band in a past subframe corresponding to the responsesignal, stored data corresponding to the downlink unit band tomodulation section 108. However, if data transmission control section307 receives DTX for a certain downlink unit band from retransmissioncontrol signal generation section 120 but did not actually transmit thedownlink data in the downlink unit band in the corresponding pastsubframe, data transmission control section 307 ignores the DTXinformation. That is, regardless of whether or not downlink data wasactually transmitted from base station 300 in a certain downlink unitband, if downlink allocation control information is not received (inthis case, downlink data is naturally not received), a response signalof terminal 400 for the downlink unit band becomes DTX. Therefore, uponreceiving DTX, data transmission control section 307 needs to performretransmission control depending on whether or not base station 300 hasactually transmitted downlink data.

Furthermore, upon receiving ACK for the downlink data transmitted in acertain downlink unit band from retransmission control signal generationsection 120, data transmission control section 307 deletes the storeddata corresponding to the downlink unit band.

[Configuration of Terminal]

Control section 409 of terminal 400 in FIG. 10 identifies PUCCHresources (frequency/code) corresponding to CCEs indicated by CCEidentification information received from decision section 208. That is,as in the cases of Embodiments 1 and 2, control section 409 identifiesPUCCH resources (that is, “basic PUCCH resources”) in a basic region ofan uplink control channel based on the CCE identification information.However, control section 409 stores information on PUCCH resources (thatis, “additional PUCCH resources”) beforehand in an additional region forchannel selection reported from base station 300 to terminal 400.

Control section 409 then determines which of basic PUCCH resources oradditional PUCCH resources are used to transmit a response signal basedon success/failure in reception of a downlink allocation control signalin each downlink unit band and error detection results on downlink datainputted from CRC section 212. That is, as in the cases of Embodiments 1and 2, control section 409 determines which of the basic PUCCH resourcesor additional PUCCH resources are used to transmit a response signalaccording to a “reception situation pattern” defined by thesuccess/failure of reception of a plurality of downlink allocationcontrol signals and error detection results regarding a plurality ofpieces of downlink data. However, unlike Embodiments 1 and 2, controlsection 409 also selects PUCCH resources based on the operation ofchannel selection even when communication without using carrieraggregation is applied to downlink data. Furthermore, control section409 further determines which constellation point is set for the responsesignal based on the above-described reception situation pattern.

[Operations of Base Station 300 and Terminal 400]

Operations of base station 300 and terminal 400 having theabove-described configurations will be described. FIG. 11, FIG. 12A andFIG. 12B are diagrams illustrating operations of base station 300 andterminal 400.

<Control on PUCCH Multiplexing Level in Unit Time/Frequency Resources byBase Station 300>

In base station 300, control section 301 sets a multiplexing level of aPUCCH signal in each PUCCH region (that is, PUCCH region a and PUCCHregion b) independently of each other.

For example, in FIG. 11, 18 PUCCH resources #1 to 18 per unittime/frequency resource are defined in PUCCH region a (that is, regionincluding PUCCH resource group associated with CCEs of preferentialdownlink unit band). On the other hand, 36 PUCCH resources #1 to 36 perunit time/frequency resource are defined in PUCCH region b (that is,additional PUCCH region reported to terminal 300). PUCCH resource 1 forterminal 400 is included in PUCCH region a and PUCCH resource 2 forterminal 400 is included in PUCCH region b.

Thus, base station 300 sets a multiplexing level per unit time/frequencyresource for each PUCCH region independently of each other as in thecases of Embodiments 1 and 2. Furthermore, PUCCH resources in PUCCHregion a are associated with CCEs in a preferential downlink unit bandin a one-to-one correspondence and information on this association isshared beforehand between base station 300 and terminal 400.

<Allocation of Downlink Data by Base Station 300>

Base station 300 determines whether or not to transmit downlink data toterminal 400 for each time unit called “subframe.” Furthermore, whentransmitting downlink data to terminal 400 in a certain subframe, basestation 300 also determines how many downlink unit bands are used(allocated). That is, when base station 300 allocates two downlink unitbands to transmit downlink data to terminal 400 in a certain subframe,base station 300 transmits downlink data using both a “preferentialdownlink unit band” set in terminal 400 and a downlink unit band otherthan the “preferential downlink unit band.” On the other hand, when onedownlink unit band is allocated in a certain subframe, base station 300transmits downlink data using only the “preferential downlink unit band”set in terminal 400. However, when there is no downlink data to betransmitted from base station 300 to terminal 400 in a certain subframe,base station 300 does not transmit downlink data in any downlink unitband.

<Reception of Downlink Data by Terminal 400>

Terminal 400 identifies a preferential downlink unit band based oninformation reported from base station 300 beforehand.

The report information on this preferential downlink unit band istransmitted through a data channel. Therefore, control section 409acquires the information on the preferential downlink unit band from thereceived data received via CRC section 212.

Furthermore, decision section 208 decides whether or not a downlinkcontrol channel of each downlink unit band includes downlink allocationcontrol information directed to the terminal and outputs the downlinkallocation control information directed to the terminal to extractionsection 204.

Extraction section 204 extracts downlink data from the received signalbased on the downlink allocation control information received fromdecision section 208.

Thus, terminal 400 can receive downlink data transmitted from basestation 300.

As in the case of Embodiments 1 and 2, downlink allocation controlinformation transmitted in downlink unit band 1 includes information onresources used to transmit downlink data (DL data) transmitted indownlink unit band 1 and downlink allocation control informationtransmitted in downlink unit band 2 includes information on resourcesused to transmit downlink data transmitted in downlink unit band 2.

Therefore, terminal 400 receives downlink allocation control informationtransmitted in downlink unit band 1 and downlink allocation controlinformation transmitted in downlink unit band 2, and can thereby receivedownlink data using both downlink unit band 1 and downlink unit band 2.On the contrary, if the terminal cannot receive downlink allocationcontrol information in a certain downlink unit band, terminal 400 cannotreceive downlink data in the downlink unit band.

<Response by Terminal 400>

CRC section 212 performs error detection on downlink data correspondingto downlink allocation control information which has been successfullyreceived and outputs the error detection result to control section 409.

Control section 409 then performs transmission control over a responsesignal based on success/failure in reception of a downlink allocationcontrol signal in each downlink unit band and the error detection resultreceived from CRC section 212 as follows.

That is, as shown in FIG. 12A and FIG. 12B, when both the errordetection result regarding downlink data transmitted in the preferentialdownlink unit band and the error detection result regarding downlinkdata transmitted in other than the preferential downlink unit band show“no error” (that is, ACK/ACK), control section 409 transmits a responsesignal using PUCCH resource 1 (that is, resources of PUCCH region a). Afirst constellation point (e.g., (I,Q)=(0,j) or the like) is used forthe response signal in this case. Furthermore, as described above, PUCCHresource 1 is determined in association with CCEs occupied by downlinkallocation control information transmitted to terminal 400 in thepreferential downlink unit band.

Furthermore, when the error detection result regarding downlink datatransmitted in the preferential downlink unit band shows “no error” andwhen downlink allocation control information is not detected in otherthan the preferential downlink unit band (that is, ACK/DTX), controlsection 409 transmits a response signal using PUCCH resource 1 (that is,resources of PUCCH region a). A second constellation point (e.g.,(I,Q)=(−1,0) or the like) is used for the response signal in this case.Similarly, when the error detection result regarding downlink datatransmitted in the preferential downlink unit band shows “no error” andthe error detection result regarding downlink data transmitted in otherthan the preferential downlink unit band shows “error present” (that is,ACK/NACK), control section 409 also transmits a response signal bysetting a second constellation point (e.g., (I,Q)=(−1,0) or the like) inPUCCH resource 1 (that is, resources of PUCCH region a).

Furthermore, when the error detection result regarding downlink datatransmitted in the preferential downlink unit band shows “error present”and downlink allocation control information is not detected in otherthan the preferential downlink unit band (that is, NACK/DTX), controlsection 409 transmit a response signal using a third constellation point(e.g., (I,Q)=(1,0) or the like) of PUCCH resource 1.

On the contrary, when downlink allocation control information is notdetected in the preferential downlink unit band and the error detectionresult regarding downlink data transmitted in other than thepreferential downlink unit band shows “no error” (that is, DTX/ACK),control section 409 sets a fourth constellation point in PUCCH resource2 (that is, resources of PUCCH region b) and transmits a responsesignal. However, the fourth constellation point may also be the sameconstellation point as one of the first to third constellation points(e.g., (I,Q)=(−1,0) or the like). Similarly, when the error detectionresult regarding downlink data transmitted in the preferential downlinkunit band shows “error present” and the error detection result regardingdownlink data transmitted in other than the preferential downlink unitband shows “no error” (that is, NACK/ACK), control section 409 also setsa fourth constellation point in PUCCH resource 2 (that is, resources ofPUCCH region b) and transmits a response signal.

Furthermore, when downlink allocation control information is notdetected in the preferential downlink unit band and the error detectionresult regarding downlink data transmitted in other than thepreferential downlink unit band shows “error present” (that is,DTX/NACK), control section 409 sets a fifth constellation point in PUCCHresource 2 (that is, resources of PUCCH region b) and transmits aresponse signal. However, the fifth constellation point may be the sameconstellation point as one of the first to third constellation points aslong as it is different from the fourth constellation point (e.g.(I,Q)=(1,0) or the like).

Thus, as also shown in FIG. 12B, one or a plurality of receptionsituation patterns are associated with three constellation points ofPUCCH resource 1 and two constellation points of PUCCH resource 2respectively. Therefore, three constellation points of QPSKconstellation points are used in PUCCH resource 1 and two constellationpoints of BPSK are used in PUCCH resource 2.

Here, the ratio of the time in which base station 300 must transmitdownlink data to terminal 400 using carrier aggregation (that is, ratioin subframe) is generally not assumed to be large. This is because whenstation 300 communicate with a sufficiently large number of terminalsbase, such a situation is unlikely to occur that only some terminalscontinue to occupy a plurality of downlink unit bands.

Therefore, when viewed from terminal 400, since the frequency with whichdownlink data is transmitted using carrier aggregation is small, thefrequency with which downlink allocation control information is detectedin downlink unit bands other than the preferential downlink unit band isalso small. That is, there are more chances that terminal 400 feeds back“DTX” to downlink unit bands other than the preferential downlink unitband.

Furthermore, as in the case of Embodiments 1 and 2, base station 300generally controls the coding rate and modulation scheme of downlinkdata so that the assumed error rate (Target Block Error Rate: TargetBLER) of downlink data becomes on the order of 0% to 30%. Therefore,when downlink allocation control information corresponding to downlinkdata on the terminal 300 side is detected, the high possibility that theresponse signal for the downlink data may be “ACK” is higher.Furthermore, as also shown in Embodiment 2, the base station controlsthe coding rate and modulation scheme of downlink allocation controlinformation so that the assumed error rate of downlink allocationcontrol information becomes on the order of 0% to 1%. Therefore, whenbase station 300 actually transmits downlink allocation controlinformation, the probability that terminal 400 may fail to receivedownlink allocation control information is very low.

From above, the probability of states that can be taken by a responsesignal for the preferential downlink unit band in a situation in whichthe terminal side should transmit a response signal (that is, asituation in which one or more pieces of downlink allocation controlinformation are detected on the terminal side) has a relationship inmagnitude expressed by equation 1 below, while the probability of statesthat can be taken by a response signal for downlink unit bands otherthan the preferential downlink unit band has a relationship in magnitudeexpressed by equation 2 below.Probability of ACK>probability of NACK>probability of DTX  (Equation 1)Probability of DTX>probability of ACK>probability of NACK  (Equation 2)

Therefore, of eight states of a response signal recognized on theterminal 400 side except DTX/DTX (that is, A/A, A/N, A/D, N/N, N/D, D/A,N/A, D/N), the state having the highest probability of occurrence is A/D(that is, a state in which, of the plurality of downlink unit bands 1and 2, no error is detected in downlink data transmitted in thepreferential downlink unit band (downlink unit band 1) and downlinkallocation control information corresponding to downlink data in adownlink unit band (downlink unit band 2) other than the preferentialdownlink unit band is not detected (that is, downlink data is nottransmitted in downlink unit band 2). Conversely, the state having thelowest probability of occurrence is D/N (that is, a state in whichdownlink allocation control information corresponding to downlink datais not detected in the preferential downlink unit band (downlink unitband 1) and downlink allocation control information in a downlink unitband (downlink unit band 2) other than the preferential downlink unitband is detected but an error is detected in the corresponding downlinkdata (pattern candidate)). This is because base station 300 transmitsdownlink data via downlink unit band 2 only when performingcommunication using carrier aggregation, and therefore the states of“D/A” and “D/N” in other words indicate that although base station 300transmits downlink data in downlink unit bands 1 and 2 (andcorresponding downlink allocation control information), the terminal 300side fails to receive downlink allocation control informationcorresponding to downlink unit band 1.

Therefore, when downlink allocation control information corresponding todownlink data is detected in the preferential downlink unit band, noerrors are detected in the downlink data and downlink allocation controlinformation corresponding to the downlink data is not detected in anydownlink unit band other than the preferential downlink unit band, abundled response signal (that is, resources used through operation ofchannel selection and response signal whose constellation point isdetermined) is transmitted using PUCCH resource 1 in PUCCH region aassociated with the downlink control channel of the preferentialdownlink unit band. Furthermore, when downlink allocation controlinformation corresponding to the downlink data is not detected in thepreferential downlink unit band, downlink allocation control informationcorresponding to the downlink data is detected in unit bands other thanthe preferential downlink unit band and an error is detected in thedownlink data, a bundled response signal is transmitted using PUCCHresource 2 in PUCCH region b. This makes it possible to suppress thefrequency with which PUCCH region b is used to a low level. Even if themultiplexing level in unit time/frequency resources included in PUCCHregion b is increased to minimize increases in overhead due to PUCCHregion b, since the frequency with which the bundled response signal ismapped to PUCCH region b is suppressed to a low level, inter-codeinterference is also prevented from increasing. It is thereby possibleto prevent deterioration of transmission characteristics of a responsesignal and minimize increases in overhead of the uplink control channel.

That is, even when a maximum allowable number of codes multiplexed isincreased to drastically reduce the number of time/frequency resourcesoccupied by an additionally required PUCCH region (that is, PUCCH regionb) resulting from carrier aggregation for resources of PUCCH region asecured in association with the control channel (that is, CCE resources)of the preferential downlink unit band, it is possible to reduce theinfluence of inter-code interference resulting from an increase of themaximum allowable number of codes multiplexed by reducing theprobability that PUCCH resource 2 may be used. As described above, areduction of the probability that PUCCH resource 2 may be used isrealized through control of channel selection using PUCCH resource 1 inthe case of ACK/DTX and using PUCCH resource 2 in the case of DTX/NACK.

The above-described effects can further be increased by mapping a stateof a relatively high probability of occurrence such as ACK/ACK orNACK/DTX to PUCCH resource 1 and mapping a state of a relatively lowprobability of occurrence such as NACK/ACK or DTX/ACK to PUCCH resource2. In other words, it is possible to maximize the effects of the presentembodiment by mapping “ACK/*” to PUCCH resource 1 (PUCCH region bassociated with the preferential downlink unit band), also “*/DTX” toPUCCH resource 1 and “DTX/*” to PUCCH resource 2 (PUCCH region bassociated with a downlink unit band other than a preferential downlinkunit band).

Moreover, although QPSK symbol points are used for PUCCH resource 1,BPSK symbol points are used for PUCCH resource 2. Thus, even wheninter-code interference in PUCCH region b slightly increases, thechannel selection state decision accuracy when using PUCCH resource 2 isless likely to deteriorate. Therefore, even if the maximum allowablenumber of codes multiplexed is increased to reduce overhead of PUCCHregion b, an adverse influence on the system is even smaller.

As described so far, according to the present embodiment, when no erroris detected in downlink data transmitted in a preferential downlink unitband and downlink allocation control information is not detected indownlink unit bands other than the preferential downlink unit band,control section 409 in terminal 400 transmits a bundled response signalusing PUCCH resource 1 in PUCCH region a associated with a downlinkcontrol channel of the preferential downlink unit band (that is,response signal whose resources used and constellation point aredetermined by operation of channel selection) and transmits a bundledresponse signal using PUCCH resource 2 in PUCCH region b when downlinkallocation control information is not detected in the preferentialdownlink unit band, downlink allocation control information is detectedin unit bands other than the preferential downlink unit band and anerror is detected in the transmitted downlink data.

By so doing, the frequency with which a bundled response signal ismapped to PUCCH region b can be made smaller than that of PUCCH regiona. Since the frequency with which a bundled response signal is mapped toPUCCH region b is reduced, it is possible to increase the multiplexinglevel of PUCCH region b and suppress increases in overhead due to PUCCHregion b to a minimum while preventing inter-code interference fromincreasing.

A case has been described above where information regarding PUCCHresource 2 is shared beforehand between base station 300 and terminal400. That is, it is assumed that information regarding PUCCH resource 2is explicitly reported from base station 300 to terminal 400. However,the present invention is not limited to this, but PUCCH resource 2 aswell as PUCCH resource 1 can be defined in association with CCEsoccupied by downlink allocation control information transmitted in otherthan the preferential downlink unit band. That is, implicit signalingfor PUCCH resource 2 may be applicable. This makes it possible to reducesignaling overhead regarding PUCCH resource 2.

Furthermore, when PUCCH resource 2 is associated with CCEs occupied bydownlink allocation control information transmitted in other than thepreferential downlink unit band, a plurality of CCEs (e.g., m continuousCCEs) in a downlink unit band other than the preferential downlink unitband may be associated with one PUCCH resource 2 in PUCCH region b toreduce the number of resources secured in PUCCH region b. This causesthe total number of PUCCH resources 2 to be defined in PUCCH region b ofthe uplink control channel to be reduced to the number of CCEs/m, whichfurther reduces PUCCH overhead.

The above descriptions presuppose that PUCCH region a including PUCCHresource 1 does not overlap with PUCCH region b including PUCCH resource2. However, the present invention is not limited to this, PUCCH region aand PUCCH region b may partially or totally overlap with each other. Inshort, it is only required that the base station side perform controlsuch that PUCCH resource 1 and PUCCH resource 2 to be recognized by acertain terminal in a certain subframe are different from each other.Base station 300 provides overlapping PUCCH region a and PUCCH region b,and can thereby reduce PUCCH overhead in the system to a levelequivalent to that of an LTE system.

Furthermore, a case has been described above where a ZAC sequence isused for primary-spreading and an orthogonal code sequence is used forsecondary-spreading. However, the present invention may also use non-ZACsequences which are mutually separable by different cyclic shift indicesfor primary-spreading. For example, GCL (Generalized Chirp like)sequence, CAZAC (Constant Amplitude Zero Auto Correlation) sequence, ZC(Zadoff-Chu) sequence, M sequence, PN sequence such as orthogonal goldcode sequence or a sequence randomly generated by a computer and havingan abrupt auto-correlation characteristic on the time axis or the likemay be used for primary-spreading. Furthermore, the ZAC sequence mayalso be expressed as a combination of a “base sequence” and a cyclicshift index in the sense that it is a sequence that becomes the basisfor applying cyclic shift processing. Furthermore, sequences orthogonalto each other or any sequences may be used as orthogonal code sequencesfor secondary-spreading as long as they are regarded as sequencessubstantially orthogonal to each other. For example, Walsh sequence orFourier sequence or the like may be used for secondary-spreading as anorthogonal code sequence. In the above descriptions, resources (e.g.,PUCCH resources) of response signals are defined by a cyclic shift indexof a ZAC sequence and an orthogonal cover index of an orthogonal codesequence.

Furthermore, the above descriptions are given assuming that base station300 always uses a preferential downlink unit band when performingcommunication without using carrier aggregation, but the presentembodiment is not limited to this. That is, when base station 300performs communication without using carrier aggregation, if thefrequency with which a preferential downlink unit band is used issufficiently greater than the frequency with which a downlink unit bandother than the preferential downlink unit band is used when performingcommunication without using carrier aggregation, above equations 1 and 2hold true and the effects described above in the present embodiment canbe obtained.

Here, features common to Embodiments 1 to 3 above will be summarized. InEmbodiments 1 to 3, the terminal transmits a bundled response signalaccording to the following response signal transmission rule. Accordingto this response signal transmission rule, success/failure in receptionof a plurality of downlink allocation control signals in the terminal,reception situation pattern candidates defined by error detectionresults regarding a plurality of pieces of downlink data and pairs ofPUCCCH resources and constellation points are associated with eachother. To be more specific, the reception situation pattern having thehighest probability of occurrence is associated with resources of afirst PUCCH region, while the reception situation pattern having thelowest probability of occurrence is associated with resources of asecond PUCCH region which is at least partially different from the firstPUCCH region. The resources in the first PUCCH region are resourcesassociated with a downlink control channel of a base unit band inEmbodiments 1 and 2 and resources associated with a downlink controlchannel of a preferential downlink unit band in Embodiment 3.

By so doing, the frequency with which a bundled response signal ismapped to the second PUCCH region can be made smaller than that of thefirst PUCCH region. Since the frequency with which a bundled responsesignal is mapped to the second PUCCH region can be suppressed to a lowlevel, it is possible to increase the multiplexing level of the secondPUCCH region and minimize increases in overhead due to the second PUCCHregion while preventing inter-code interference from increasing.

Other Embodiments

(1) Taking notice in Embodiments 1 to 3 that there is a high possibilitythat the terminal side may fail to receive downlink allocation controlinformation and downlink data, and further taking notice in Embodiment 3that the frequency with which the base station performs communicationwith the terminal using carrier aggregation is small, the probability ofuse of resources of PUCCH region 1 (or a) is set to be as high aspossible and the frequency with which resources of PUCCH region 2 (orb)are used is set to be as low as possible. However, similar effects canalso be obtained through mapping that suppresses the difference betweenthe probability of use of resources of PUCCH region 1 (or a) and theprobability of use of resources of PUCCH region 2 (orb) to the order ofseveral times.

This will be described by taking Embodiment 3 as an example. When aprobability that a response signal for a preferential downlink unit bandmay be ACK, NACK, DTX is assumed to be 89%, 10%, 1% respectively and aprobability that a response signal for a downlink unit band other thanthe preferential downlink unit band may be DTX, ACK, NACK is assumed tobe 90%, 9%, 1% respectively, the probability of use of resources ofPUCCH region b in FIG. 12B is on the order of 1%. That is, there is toolarge a difference between the probability of use of resources of PUCCHregion b and the probability of use of resources of PUCCH region a.Therefore, as shown in FIG. 13, it is also useful to adopt mapping thatsuppresses the difference in frequency of use between the resources ofPUCCH region a and the resources of PUCCH region b to within severaltimes by shifting the reception situation pattern with a relatively highfrequency such as ACK/ACK and NACK/DTX to the resources of PUCCH regionb. That is, while considering various factors under a condition thatACK/DTX having the highest probability of occurrence of the receptionsituation pattern is mapped to resources of PUCCH region a, suchapplication is possible that other reception situation patterns aremapped to one of a plurality of PUCCH regions so as to optimize thebalance in difference in frequency of use of the PUCCH region. Theusefulness of optimizing balance in frequency of use between PUCCHregions also applies to Embodiments 1 and 2.

(2) A case has been described in Embodiments 1 and 2 where a maximumallowable number of codes multiplexed in unit time/frequency resourcesis independently determined for a basic region including basic PUCCHresources and an additional region including additional PUCCH resourcesand the maximum allowable number of codes multiplexed of the basicregion is smaller than that of the additional region. That is, moreboxes for accommodating PUCCH signals (that is, PUCCH resources) areprovided in unit time/frequency resources of the additional region thanin unit time/frequency resources of the basic region.

However, the present invention is not limited to this, but it is onlynecessary that the maximum allowable number of codes multiplexed of thebasic region be substantially smaller than that of the additionalregion.

For example, even if the same number of positions used out of positionsused as cyclic shift indices is set for the basic region and theadditional region, if all of the following conditions (a) to (c) aresatisfied, the assumed maximum number of codes multiplexed in the basicregion is substantially smaller than the maximum number of codesmultiplexed in the additional region.

(a) PUCCH resources in the basic region are associated with CCEs of thebase unit band in a one-to-one correspondence and PUCCH resources to beused are determined from the CCE number occupied by “downlink allocationcontrol information received by the terminal.” That is, PUCCH resourcesare implicitly reported.

(b) Regarding PUCCH resources in the additional region, resource numbersto be used are explicitly reported from the base station to theterminal.

(c) One L1/L2 CCH may occupy a plurality of CCEs and one L1/L2 CCHreports allocation information of one piece of downlink data.

By satisfying all conditions (a) to (c), the assumed maximum number ofcodes multiplexed in the basic region is substantially smaller than themaximum number of codes multiplexed of the additional region for thefollowing reasons. That is, in the additional region, the base stationcan allocate all PUCCH resources to different terminals, whereas in thebasic region, although one L1/L2 CCH occupies a plurality of CCEs, sinceone L1/L2 CCH is used to report only one piece of downlink data, someCCEs remain unused. This situation becomes more noticeable when CCEs areused not only to transmit downlink allocation control information butalso to transmit uplink allocation control information for reportinguplink resources to be used for uplink data from the terminal. The PUCCHregion associated with the downlink control channel of the preferentialdownlink unit band and the PUCCH region associated with the downlinkcontrol channel of the downlink unit band other than the preferentialdownlink unit band in Embodiment 3 can also be treated the same as theabove-described basic region and additional region.

(3) A case has been described in the above-described embodiments wheretwo downlink unit bands are included in a unit band group in asymmetriccarrier aggregation configured for the terminal. However, the presentinvention is not limited to this and three or more downlink unit bandsmay be included in the unit band group. In this case, PUCCH regionscorresponding to the respective downlink unit bands are definedseparately.

(4) A case has been described in the above-described embodiments whereonly one uplink unit band is included in a unit band group in asymmetriccarrier aggregation configured for the terminal, and the basic PUCCHresources and the additional PUCCH resources are included in the sameuplink unit band. However, the present invention is not limited to this,but a plurality of uplink unit bands may be included in the unit bandgroup and the basic PUCCH resources and the additional PUCCH resourcesmay be defined in different uplink unit bands.

(5) Only asymmetric carrier aggregation has been described in theabove-described embodiments. However, the present invention is notlimited to this, but the present invention is also applicable to a casewhere symmetric carrier aggregation is set with respect to datatransmission. In short, the present invention is applicable to any casewhere a plurality of PUCCH regions are defined in uplink unit bandsincluded in the unit band group of the terminal and a PUCCH regionincluding PUCCH resources to be used is determined according to thesituation of success/failure in reception of downlink data.

(6) A case has been described in the above-described embodiments wherethe control section (101, 301) of the base station performs control suchthat downlink data and downlink allocation control informationcorresponding to the downlink data are mapped to the downlink unit band,but the present invention is not limited to this. That is, even ifdownlink data and downlink allocation control information correspondingto the downlink data are mapped to different downlink unit bands, thedownlink data and downlink allocation control information correspondingto the downlink data need not always be mapped to the same downlink unitband as long as the correlation between the downlink allocation controlinformation and downlink data is clear. In this case, the terminal sideobtains PUCCH resources as the PUCCH resources associated with the“resources (CCE) occupied by downlink allocation control information(which is not necessarily present in the same downlink unit band as thedownlink data) corresponding to downlink data transmitted in thecorresponding downlink unit band.”

(7) Furthermore, the ZAC sequence in the above-described embodiments mayalso be referred to as “base sequence” in the sense that it is asequence that serves as the basis for applying cyclic shift processing.

Furthermore, the Walsh sequence may also be referred to as “Walsh codesequence.”

(8) Furthermore, a case has been described in the above-describedembodiments where secondary-spreading is performed afterprimary-spreading and IFFT transform as the order of processing on theterminal side. However, the order of processing is not limited to this.That is, since both primary-spreading and secondary-spreading aremultiplication processing, an equivalent result may be obtainedregardless of the location of secondary-spreading processing as long asIFFT processing follows primary-spreading processing.

(9) Furthermore, since the spreading section according to theabove-described embodiments performs processing of multiplying a certainsignal by a sequence, the spreading section may also be called a“multiplication section.”

(10) Moreover, although cases have been described with the embodimentsabove where the present invention is configured by hardware, the presentinvention may be implemented by software.

Each function block employed in the description of the aforementionedembodiment may typically be implemented as an LSI constituted by anintegrated circuit. These may be individual chips or partially ortotally contained on a single chip. “LSI” is adopted here but this mayalso be referred to as “IC,” “system LSI,” “super LSI” or “ultra LSI”depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSI's, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of an FPGA (FieldProgrammable Gate Array) or a reconfigurable processor where connectionsand settings of circuit cells within an LSI can be reconfigured is alsopossible.

Further, if integrated circuit technology comes out to replace LSI's asa result of the advancement of semiconductor technology or a derivativeother technology, it is naturally also possible to carry out functionblock integration using this technology. Application of biotechnology isalso possible.

The disclosures of Japanese Patent Application No. 2009-146592, filed onJun. 19, 2009 and Japanese Patent Application No. 2009-252051, filed onNov. 2, 2009, including the specifications, drawings and abstracts, areincorporated herein by reference in their entirety.

INDUSTRIAL APPLICABILITY

When ARQ is applied to communication using an uplink unit band and aplurality of downlink unit bands associated with the uplink unit band,the terminal apparatus and retransmission control method according tothe present invention are useful as being able to prevent deteriorationof transmission characteristics of a response signal and suppressincreases in overhead of an uplink control channel to a minimum.

REFERENCE SIGNS LIST

-   -   100 base station    -   101,209,301,409 control section    -   102,302 control information generation section    -   103, 106 coding section    -   104, 108, 214 modulation section    -   105 broadcast signal generation section    -   107, 307 data transmission control section    -   109 mapping section    -   110, 217 IFFT section    -   111, 218 CP adding section    -   112, 219 radio transmitting section    -   113, 201 radio receiving section    -   114, 202 CP removing section    -   115 PUCCH extraction section    -   116 despreading section    -   117 sequence control section    -   118 correlation processing section    -   119, 208 decision section    -   120 retransmission control signal generation section    -   200 terminal    -   203 FFT section    -   204 extraction section    -   205 broadcast signal receiving section    -   206, 210 demodulation section    -   207, 211 decoding section    -   212 CRC section    -   213 response signal generation section    -   215 primary-spreading section    -   216 secondary-spreading section

The invention claimed is:
 1. A terminal, comprising: circuitry, which,in operation, detects control information on a control channel element(CCE), the control information including downlink assignment informationthat indicates a downlink data resource assigned to one of a pluralityof configured downlink component carriers, the plurality of configureddownlink component carriers including at least a first downlinkcomponent carrier and a second downlink component carrier to whichrespective downlink data resources are assigned by the respectivecontrol information; decodes the control information; and decodesdownlink data in the respective downlink data resources; and atransmitter, which, in operation, transmits respective response signalsto the downlink data, wherein: a response signal is transmitted usingone of a first uplink control channel resource, an index of which isassociated with a CCE number of the CCE, or a second uplink controlchannel resource, an index of which is signaled to the terminal,depending on a combination of an Acknowledgement (ACK) representing asuccessful outcome of decoding the control information, a NegativeAcknowledgment (NACK) representing an unsuccessful outcome of decodingthe control information, and a Discontinuous Transmission (DTX)representing that an outcome of decoding the control information is nottransmitted, for the control information on the first downlink componentcarrier and for the control information on the second downlink componentcarrier.
 2. The terminal according to claim 1, wherein the first uplinkcontrol channel resource is used when the control information on thefirst downlink component carrier is detected and the control informationon the second downlink component carrier is not detected, and the seconduplink control channel resource is used when the control information onthe first downlink component carrier is not detected and the controlinformation on the second downlink component carrier is detected.
 3. Theterminal according to claim 1, wherein the response signals denote oneof: an outcome of a decoding of the downlink data on the respectivedownlink component carrier(s); and a Discontinuous Transmission (DTX)representing that the outcome is not transmitted.
 4. The terminalaccording to claim 3, wherein when a response signal denotes the DTX fordownlink data on the second downlink component carrier, the transmitter,in operation, transmits the response signal using the first uplinkcontrol channel resource.
 5. The terminal according to claim 3, whereinwhen a response signal denotes the DTX for downlink data on the firstdownlink component carrier, the transmitter, in operation, transmits theresponse signal using the second uplink control channel resource.
 6. Theterminal according to claim 3, wherein when a response signal denotesthe outcome for downlink data on the first downlink component carrierand denotes an unsuccessful decoding or the DTX for downlink data on thesecond downlink component carrier, the transmitter, in operation,transmits the response signal using the first uplink control channelresource.
 7. The terminal according to claim 3, wherein when a responsesignal denotes the outcome for downlink data on the second downlinkcomponent carrier and denotes the DTX for downlink data on the firstdownlink component carrier, the transmitter, in operation, transmits theresponse signal using the second uplink control channel resource.
 8. Theterminal according to claim 3, wherein when a response signal denotes asuccessful decoding for downlink data on the second downlink componentcarrier and denotes an unsuccessful decoding or the DTX for downlinkdata on the first downlink component carrier, the transmitter, inoperation, transmits the response signal using the second uplink controlchannel resource.
 9. The terminal according to claim 1, wherein thefirst downlink component carrier is a primary component carrier.
 10. Theterminal according to claim 1, wherein the transmitter, in operation,transmits the response signal on a single uplink component carrier. 11.The terminal according to claim 1, wherein the response signals denotean outcome of a decoding in the terminal by one of an Acknowledgment(ACK) and a Negative Acknowledgment (NACK).
 12. The terminal accordingto claim 1, wherein at least one response signal denotes a DiscontinuousTransmission (DTX) that represents that downlink assignment informationcorresponding to the downlink data is not detected by the circuitry. 13.The terminal according to claim 1, wherein the first uplink controlchannel resource index is implicitly signaled to the terminal, and thesecond uplink control channel resource index is explicitly signaled tothe terminal.
 14. A terminal, comprising: circuitry, which, inoperation, detects control information on a control channel element(CCE), the control information including downlink assignment informationthat indicates a downlink data resource assigned to one of a pluralityof configured downlink component carriers, the plurality of configureddownlink component carriers including at least a first downlinkcomponent carrier and a second downlink component carrier to whichrespective downlink data resources are assigned by the respectivecontrol information; decodes the control information; and decodesdownlink data in the respective downlink data resources; and atransmitter, which, in operation, transmits respective response signalsto the downlink data, wherein: a response signal is transmitted usingone of a first uplink control channel resource, an index of which isassociated with a CCE number of the CCE, or a second uplink controlchannel resource, an index of which is signaled to the terminal,depending on a combination of an Acknowledgement (ACK) representing asuccessful outcome of decoding the control information, a NegativeAcknowledgment (NACK) representing an unsuccessful outcome of decodingthe control information, and a Discontinuous Transmission (DTX)representing that an outcome of decoding the control information is nottransmitted, for the control information corresponding to downlink dataon the first downlink component carrier and for the control informationcorresponding to downlink data on the second downlink component carrier.15. The terminal according to claim 14, wherein the first uplink controlchannel resource is used when the control information corresponding todownlink data on the first downlink component carrier is detected andthe control information corresponding to downlink data on the seconddownlink component carrier is not detected, and the second uplinkcontrol channel resource is used when the control informationcorresponding to downlink data on the first downlink component carrieris not detected and the control information corresponding to downlinkdata on the second downlink component carrier is detected.
 16. A method,comprising: detecting, by a terminal, control information on a controlchannel element (CCE), the control information including downlinkassignment information that indicates a downlink data resource assignedto one of a plurality of configured downlink component carriers, theplurality of configured downlink component carriers including at least afirst downlink component carrier and a second downlink component carrierto which respective downlink data resources are assigned by therespective control information; decoding the control information;decoding downlink data in the respective downlink data resources; andtransmitting respective response signals to the downlink data, wherein:a response signal is transmitted using one of a first uplink controlchannel resource, an index of which is associated with a CCE number ofthe CCE, or a second uplink control channel resource, an index of whichis signaled to the terminal, depending on a combination of anAcknowledgement (ACK) representing a successful outcome of decoding thecontrol information, a Negative Acknowledgment (NACK) representing anunsuccessful outcome of decoding the control information, and aDiscontinuous Transmission (DTX) representing that an outcome ofdecoding the control information is not transmitted, for the controlinformation on the first downlink component carrier and for the controlinformation on the second downlink component carrier.
 17. The methodaccording to claim 16, wherein the first uplink control channel resourceis used when the control information on the first downlink componentcarrier is detected and the control information on the second downlinkcomponent carrier is not detected, and the second uplink control channelresource is used when the control information on the first downlinkcomponent carrier is not detected and the control information on thesecond downlink component carrier is detected.
 18. A method, comprising:detecting, by a terminal, control information on a control channelelement (CCE), the control information including downlink assignmentinformation that indicates a downlink data resource assigned to one of aplurality of configured downlink component carriers, the plurality ofconfigured downlink component carriers including at least a firstdownlink component carrier and a second downlink component carrier towhich respective downlink data resources are assigned by the respectivecontrol information; decoding the control information; decoding downlinkdata in the respective downlink data resources; and transmittingrespective response signals to the downlink data, wherein: a responsesignal is transmitted using one of a first uplink control channelresource, an index of which is associated with a CCE number of the CCE,or a second uplink control channel resource, an index of which issignaled to the terminal, depending on a combination of anAcknowledgement (ACK) representing a successful outcome of decoding thecontrol information, a Negative Acknowledgment (NACK) representing anunsuccessful outcome of decoding the control information, and aDiscontinuous Transmission (DTX) representing that an outcome ofdecoding the control information is not transmitted, for the controlinformation corresponding to downlink data on the first downlinkcomponent carrier and for the control information corresponding todownlink data on the second downlink component carrier.
 19. The methodaccording to claim 18, wherein the first uplink control channel resourceis used when the control information corresponding to downlink data onthe first downlink component carrier is detected and the controlinformation corresponding to downlink data on the second downlinkcomponent carrier is not detected, and the second uplink control channelresource is used when the control information corresponding to downlinkdata on the first downlink component carrier is not detected and thecontrol information corresponding to downlink data on the seconddownlink component carrier is detected.